Questions 31 to 35 are based on the following passage:
Judging from recent surveys, most experts in sleep behavior agree that there is virtually an
epidemic(流行病) of sleepiness in the nation. "I can't think of a single study that hasn't
found Americans getting less sleep than they ought to," says Dr. David. Even people who think
they are sleeping enough would probably be better off with more rest.
The beginning of our sleep - deficit (睡眠不足) crisis can be traced to the invention of the
light bulb a century ago. From diary entries and other personal accounts from the 18th and 19th
centuries sleep scientists have reached the conclusion that the average person used to sleep
about 9.5 hours a night. "The best sleep habits once were forced on us, when we had nothing to
do in the evening down on the farm, and it was dark. "By the 1950s and 1960s, that sleep
schedule had been reduced dramatically, to between 7.5 and eight hours, and most people had
to wake to an alarm clock. "People cheat on their sleep, and they don't even realize they' re doing it, "says Dr. David. "They think they' re okay because they can get by on 6.5 hours, when
they really need 7.5, eight or even more to feel ideally vigorous."
Perhaps the most merciless robber of sleep, researchers say, is the complexity of the day.
Whenever pressures from work, family, friends and community mount, many people consider
sleep the least expensive item on his programme. "In our society, you' re considered dynamic if
you say you only need 5.5 hours' sleep. If you've got to get 8.5 hours, people think you lack
drive and ambition."
To determine the consequnces of sleep deficit, researchers have put subjects through a set
of psychological and performance tests requiring them, for instance, to add columns of numbers
or recall a passage read to th
[page][page]hem only minutes earlier. "We' ye found that if you' re in sleep
deficit, performance suffers, "says Dr. David. "Short - term memory is weakened, as are abilities
to make decisions and to concentrate."
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